WEEDY ADAPTATION SETARIA SPP .4. CHANGES IN THE GERMINATIVE CAPACITY OF S-FABERII (POACEAE) EMBRYOS WITH DEVELOPMENT FROM ANTHESIS TO AFTERABSCISSION

Studies were conducted evaluating germinability states in giant foxtai l (Setaria faberii) embryos, as well as surrounding tissues (hull, car yopsis), with germination assays. Further, seed age, fascicle arrangem ent, flowering patterns, and elongation in the inflorescence were eval uated. Both qualitatitive and quantitative morphological observations of the hull and the caryopsis were revealed by precisely determined fe rtilized spikelet age from anthesis until after seed abscission. Red c oloration of the placental pad at approximate to 11 d after anthesis i s probably a morphological indicator of physiological maturity. Germin ability of giant foxtail embryos changed with development. Four qualit atively different types of embryo germination were observed during dev elopment of the seed: early disorganized callus growth at the basal, c oleorhizal end of the embryo; germination of immature embryos with sho rtened and thickened axes; germination of the scutellum; and germinati on and growth of the coleoptile and coleorhiza in embryos aged 7 d aft er anthesis and older. Axis-specific embryo germinability was also obs erved. Inhibition of the embryo could be localized to the coleoptile, the coleorhiza, or both. These studies provide evidence for a complex model of germinability regulation based on the independent, asynchrono us actions of the embryo, caryopsis, and hull compartments, as well as on their dependent, synchronous action. These studies provide evidenc e for a dynamic, developmental model of giant foxtail germinability re gulation resulting in phenotypes with a wide range of germinability sh ed from an individual panicle. These diverse germinability phenotypes are found at all stages of development, but particularly when the seed is shed and the soil seed bank is replenished.